1. Field of the Invention
The present invention relates to a method of form an annular collar that essentially radial on a hollow annular end portion of a part, and to a method of retaining a bearing on the outside surface of a shaft, and to an assembly comprising a shaft and a bearing.
2. Description of the Related Art
The invention is typically applicable for retaining a bearing on a hub or a stub of a wheel of a motor vehicle, so as to enable it to be rotated.
To achieve such retention, it is known that a nut-and-bolt system can be used which, by applying a tightening force between the hub and the inner ring of the bearing, makes it possible firstly to retain the bearing and secondly to adjust the applied pre-load.
Such systems suffer, in particular, from the drawback of requiring a step of adjusting the pre-load during assembly. In addition, due to the nut loosening, they are liable not to provide a constant pre-load throughout the life span of the bearing.
To solve those drawbacks, “ready-to-use” bearings have been proposed that, by manufacture, are held stationary on the outside surface of the hub, thereby providing the pre-load without subsequent adjustment being necessary. Such retention is obtained, in particular, after disposing the bearing on the hub, by forming a radial collar on the free end of the hub.
To form such a collar, it is known that it is possible to use a method in one deformation step during which a tool having the overall shape of the collar to be formed is put in rotating contact with the free end of the hub or of the stub.
Such methods suffer, in particular, from the drawback of requiring large forces to be applied to the free end so as to push back the material forming the collar.
Unfortunately, for forming collars of size sufficient to withstand the operating stresses, it is frequent for the forces applied to damage the bearings.
In particular, residual stresses at the raceways can appear because of the rings swelling due to the forces applied. Such stresses give rise to a reduction in the life span of the bearings by them flaking or breaking prematurely.
In addition, with methods in a single deformation step, it is difficult to apply a retaining tension that is sufficient between the bearing and the outside surface of the hub, i.e. to press the inner ring against the outside surface of the hub or of the stub.
Finally, forming a substantially plane face on the free lateral face of the collar, although necessary to guarantee correct abutment against another part, is difficult to obtain with the prior art methods in one deformation step.